To make the dipping sauce, add the dashi, soy sauce, sake and sugar to a saucepan, and bring the mixture to a boil. Continue boiling for 1 minute to vaporize the alcohol in the sake and soy sauce. Set this aside to cool.
To boil the soba noodles, bring a large pot of water to a rolling boil. Add the soba noodles and stir for about a minute to ensure the noodles don't stick together. Continue boiling the noodles for the amount of time specified on the package.
Transfer the noodles to a strainer using chopsticks or tongs (leaving the boiling liquid in the pot).
Wash the soba under cold running water to cool it to room temperature while removing any excess starch on the noodles' surface.
Transfer the soba to a bowl of ice water and let the noodles chill for a moment.
Serve the noodles by scooping small amounts of soba out of the ice water and bundling them up into small mounds on a zaru or large flat basket.
Serve immediately with the dipping sauce and condiments.
Once you've finished eating the cold soba, reheat the boiling liquid and serve it in a teapot to add to the remaining dipping sauce to make a broth.
